Method and device for assembling substrates

ABSTRACT

A method and apparatus for joining at least two substrates together, especially to form an optical data carrier, are provided. Substrates are disposed in a spaced-apart manner between two plates that are disposed opposite from, and are movable relative to, one another. At least one of the plates is connected to a flexible membrane. At least the plate to which the flexible membrane is connected is moved in such a way that a pressure difference is produced on opposite sides of the membrane.

[0001] The present invention relates to a method and an-apparatus forjoining at least two substrates together, especially for forming anoptical data carrier, according to which the substrates are disposed ina spaced-apart state between two oppositely disposed plates that aremovable toward one another.

[0002] An apparatus of this type is known, for example, from the notpre-published DE 199 27 516.5 that originates with the same applicant.With the known apparatus, a double-sided adhesive foil or film is firstapplied to a first substrate. Subsequently, the substrate, with theadhesive film facing upwardly, is placed upon a first plate. Provided onthe first plate is a centering pin, that is introduced into an innerhole of the substrate and centers it. Subsequently, a second substrateis positioned over the first substrate and, by suitable noses of thecentering pin, is held parallel to and spaced above the first substrate.Subsequently, a closed chamber is formed about the substrate and issupplied with underpressure. When a desired pressure is achieved, apressure ram disposed in the chamber is moved downwardly in order topress the two substrates together and glue them to one another. Afterthe pressing together, the adhesive film disposed between the substratesis cured in a suitable manner.

[0003] With this apparatus there results the problem that the supportplate and the pressure ram must be parallel to one another in order touniformly join the two substrates together, which significantlyincreases the complexity and the cost for the apparatus.

[0004] Proceeding from the aforementioned state of the art, it istherefore an object of the present invention to provide a method and anapparatus for joining substrates together according to which the uniformjoining of the substrates together is possible in a straightforward andeconomical manner.

[0005] Pursuant to the invention, this object is realized with a methodfor joining at least two substrates together, especially for forming anoptical data carrier, according to which the substrates are disposedspaced apart between two oppositely disposed plates that are movablerelative to one another, in that at least one of the plates, which isconnected with a flexible membrane, is moved in such a way that apressure difference is produced on opposite sides of the membrane. Bymounting one of the plates on a flexible membrane, there results afloating mounting of the plate, which during the joining of thesubstrates together enables a good and uniform conformation of the twoplates relative to one another. This ensures a uniform pressing togetherof the substrates. Furthermore, by producing a relatively small pressuredifference on opposite sides of the membrane, a high pressure can beachieved.

[0006] Pursuant to one preferred embodiment of the invention, thepressure difference is achieved by applying an underpressure in a firstchamber that surrounds the plates, whereby one wall of the chamber isformed at least partially by the membrane. By producing theunderpressure in the first chamber that surrounds the plates, on the onehand the required pressure difference is produced, and on the other handthe joining of the substrates together is effected under underpressureconditions that considerably reduce the risk of air bubbles between thesubstrates.

[0007] An underpressure is preferably applied in a second chamber, whichis disposed on a side of the membrane that faces away from the plates,in order to initially keep the membrane, and the plate mounted thereon,spaced from the other plate. In this connection, prior to the joining ofthe substrates together the pressure in the second chamber is preferablykept below the pressure in the first chamber in order to prevent theplates from prematurely moving toward one another in an uncontrolledmanner. Pursuant to one preferred embodiment of the invention, thepressure in the second chamber is brought to ambient pressure for thejoining of the substrates together, while the pressure in the firstchamber is kept at an underpressure. The pressure in the second chambercan be brought to ambient pressure in a controlled manner, as a resultof which a movement of the two plates toward one another is controlled.This ensures a uniform joining of the substrates together.

[0008] After the joining of the substrates together, the first chamberis preferably supplied with pressure to separate the plates from oneanother. The pressure in the first chamber furthermore effects a curingor hardening of an adhesive disposed between the substrates.

[0009] Pursuant to a particularly preferred embodiment of the invention,prior to being joined together the substrates are held spaced from oneanother by a centering pin that engages in an inner hole of thesubstrates, as a result of which on the one hand, a centering of thesubstrates relative to one another is provided, and also an undesiredand uncontrolled joining of the substrates together is prevented.

[0010] The object of the present invention is also realized with anapparatus for joining at least two substrates together, especially forforming an optical data carrier, and includes two oppositely disposedplates that are movable relative to one another for pressing thesubstrates together, and that at least one of the plates is connectedwith a flexible membrane, and a device is provided for producing apressure difference on opposite sides of the membrane. By connecting oneof the plates with a flexible membrane, there results the already abovedescribed advantages that the plate is floatingly mounted and thus agood conformation is possible to the other plate. Furthermore, byproducing a slight pressure difference on opposite sides of themembrane, a good pressure can be achieved since the pressure differenceacts on a relatively large surface comprised of plate and membrane.

[0011] A first, essentially closed chamber is preferably formed on afirst side of the membrane in order to be able to produce a pressuredifference on the opposite sides of the membrane. Pursuant to thepreferred embodiment of the invention, a second, essentially closedchamber is preferably provided on a second side of the membrane in orderto ensure a good controllability of the pressure difference.

[0012] At least one vacuum source is advantageously provided that can beconnected with the first and/or second chamber. The vacuum source is ina position to produce the desired pressure difference, as well as toenable a joining of the substrates together in a low-pressureatmosphere, as a result of which air bubbles between the substrates areavoided.

[0013] Pursuant to the preferred embodiment of the invention, at leastone pressure source is furthermore provided that can be connected withthe first and/or second chamber in order to produce the desired pressuredifference, or in order to hold the substrates in a pressure atmosphereafter the joining together and to cure an adhesive disposed between thesubstrates.

[0014] The plates are preferably disposed together in one of thechambers. To limit the movement of the membrane and the plate in adirection away from the other plate, a support or abutment means ispreferably provided on that side of the membrane that faces away fromthe plates. As a result of the movement limitation, the service life ofthe membrane can be considerably prolonged, since a deflection isessentially effected in only one direction.

[0015] For a good and uniform loading of the membrane, and a goodconformation of the plates relative to one another, they are preferablydisposed essentially horizontally. In this connection, the plate that ismounted on the membrane is advantageously disposed above the otherplate. This arrangement makes it possible that a single plate mounted ona membrane cooperates with a plurality of plates that are provided, forexample, on a rotary switching or indexing table. In this way, thethroughput of the apparatus is increased while at the same time reducingcosts. By using the same membrane, successive, uniform processingresults can furthermore be produced. In this connection, the membrane ispreloaded upwardly against a support or abutment means by an elasticelement, especially a spring.

[0016] Preferably provided on one of the plates is a centering pin thatcan be introduced into an inner hole of the substrates in order tocenter them relative to one another during the joining together. Toensure a controlled joining of the substrates together, the centeringpin preferably keeps the substrates spaced apart and essentiallyparallel to one another prior to the substrates being joined together.

[0017] The inventive method and the apparatus are particularly suitablefor optical recording media, such as CD's, DVD's, etc., where twosubstrates are glued together to form the data carrier. It is, ofcourse, also possible to join a plurality of substrates together in theaforementioned manner. The inventive method and the apparatus arepreferably used in combination with an apparatus according to whichprior to the joining of the substrates together, a double-sided adhesivefoil or film is applied to one of the substrates, as is known, forexample, from the not pre-published DE 199 27 516.5, which originatesfrom the same applicant and which in this connection is made the subjectmatter of the present invention in order to avoid repetition.

[0018] The invention will be described in greater detail subsequentlywith the aid of preferred embodiments with reference to the figures.Shown are:

[0019]FIG. 1 a schematic cross-sectional view through one apparatus, forthe joining of substrates together, in a first position prior to thejoining of the substrates together;

[0020]FIG. 2 a schematic cross-sectional view through the apparatus ofFIG. 1 in a second position during the joining of the substratestogether;

[0021]FIG. 3 a schematic illustration of a centering pin used in theapparatus of FIG. 1;

[0022]FIG. 4 a schematic illustration of an alternative embodiment of anapparatus for the joining of substrates together.

[0023]FIG. 1 shows an apparatus 1 for the joining together of twosubstrates 3, 4, which have an inner hole and form, for example, a CD orDVD or some other data carrier. FIG. 1 shows the apparatus in a positionprior to the joining of the substrates 3,4 together. In order, duringthe joining of the substrates 3,4 together, to ensure a gluing togetherthereof, as can be seen in FIG. 1 an adhesive 5 in the form of adouble-sided adhesive foil or film is applied to the substrate 4. Thedouble-sided adhesive film, as well as an appropriate device forapplying the adhesive film, is known, for example, from the notpre-published DE 199 27 516.5, which originates with this same applicantand which to this extent is made the subject matter of the presentinvention in order to avoid repetition.

[0024] The apparatus 1 has a housing 7, which is formed from two housingportions 9, 10 that are movable relative to one another and which eachhave an essentially U-shaped cross-section. In a moved-together state,the two housing portions 9,10 form a chamber 12 between them. Thechamber 12 is sealed relative to the surroundings at the interface 14between the two housing portions 9,10.

[0025] In the housing portion 10, which pursuant to FIG. 1 representsthe lower housing portion, there is provided a flexible membrane 16 ofsynthetic or plastic material that completely spans the inner region ofthe housing portion 10 and as a result divides the chamber 12 that isformed between the housing portions 9,10 into an upper chamber portion18 and a lower chamber portion 19. Of course, the membrane 16 can alsobe made of some other suitable material, such as, for example, metal.The lower chamber portion 19 can be supplied with underpressure via avacuum source 22, such as a vacuum pump, and an appropriate conduit 23in the housing portion 10, as will be described in greater detailsubsequently. In the same manner, the upper chamber portion 18 can besupplied with underpressure via a vacuum source 26 and an appropriateconduit 27 in the upper housing portion 9. The upper chamber portion 18can furthermore be supplied with pressure via a pressure source 30, suchas a pump, and an appropriate conduit 31 in the upper housing portion 9.The function of the vacuum sources as well as of the pressure sourcewill be described in greater detail subsequently.

[0026] Mounted in a suitable manner to the membrane 16 is a plate 34that faces the upper chamber portion 18, so that the plate 34 is movablewith the flexible membrane 16. The plate 34 can, for example, be gluedto the membrane 16, or the plate 34, and a non-illustrated clamping orretaining ring, can clamp the membrane 16 between them. Provided on theplate 34 is a centering pin 36 that will be described in greater detailsubsequently with reference to FIG. 3.

[0027] Provided on the upper housing portion 9 is a plate 38 that isdisposed opposite to the plate 34. The plate 38 has a central opening 40into which the centering pin 36 is movable during a movement of thelower plate 34 toward the upper plate 38, as illustrated in FIG. 2.

[0028] The plates 34 and 38 have a geometry that is adapted to thesubstrates. In FIG. 1, the plate 38 is illustrated as a separatecomponent that is mounted on the housing portion 9. Of course, the platecan also be integrally or monolithically formed with the housing portion9, or the inner wall of the inner housing 9 can serve as a plate orcooperating surface for the lower plate 34, so that an additional plate,such as the plate 38, is eliminated.

[0029] Provided in the lower chamber portion 19 are two abutment orsupport means 42 that are essentially disposed below the plate 34. Thesupport means limit a movement of the membrane 16 and the upper plate 34in a downwardly directed direction, as a result of which the membrane 16essentially deflects only upwardly, which prolongs its service life.Instead of two support means, it is, of course, also possible to provideonly one support means 42, preferably centrally arranged. The supportmeans can also be arranged in such a way that they do not overlapregions of the membrane 16 that are covered by the plate 34 in order toabsorb the forces that act upon the membrane 16 in this region.

[0030] The construction of the centering pin 36 will be described ingreater detail with reference to FIG. 3. The construction of thecentering pin is described in greater detail in the not pre-published DE199 27 514.9, which originates with the applicant and which to thisextent is made the subject matter of the present invention in order toavoid repetition. The centering pin 36 has an upwardly open hollow space45 that is limited to the side by a circumferential side wall 47 andtoward the bottom by a base 48 of the pin 36. The outer periphery of thewall 47 is adapted to the shape of the inner holes of the substrates3,4, and in particular in a lower region the pin has a precisely groundouter periphery in order to ensure a good centering and guidance of thetwo substrates 3,4. The upper end of the wall 47 is chamfered, so thatit defines an upwardly tapering bevel 49. The bevel 49 enables acentering and guidance of the substrates as they are received upon thepin 36.

[0031] Mounted on the side wall 47 of the pin 36 is a plurality ofmovable noses 50, two of which are illustrated in FIG. 3. With thepresently preferred embodiment four noses 50 are provided. The noses 50are pivotably mounted in a suitable manner on the wall 47 of the pin 36in order to enable a movement of the noses between the positions shownin FIGS. 1 and 2.

[0032] The noses 50 are preloaded by compression springs 52 radiallyoutwardly away from the pin 36 into the position shown in FIG. 3, andare pivotable against this spring preload into the position shown inFIG. 2. Provided in the hollow space 45 of the pin 36 is a cone 53 thattapers upwardly and is movable within the hollow space 45. The cone 45is preloaded upwardly by a spring 55 into the position shown in FIG. 3.

[0033] One end of the compression springs 52 is supported against thecone 53, and the other end thereof is supported against the noses 50 inorder to press them outwardly. The springs 52 can slide along theconical surface of the cone 63 when the latter is pressed downwardlyagainst the preload of the spring 55, as a result of which the outwardlydirected preload force is varied.

[0034] The noses 50 have linear outer surfaces against which thesubstrates can slide downwardly, and which enable a precise guidance ofthe substrates. If a first substrate 4, with an adhesive layer 5disposed thereon, is moved into the position shown in FIG. 3, a secondsubstrate 3 can be placed upon the noses 50. Due to the fact that thenoses 50 are preloaded radially outwardly, they hold the substrate 3 inthe illustrated position, in which it is spaced relative to the firstsubstrate 4. Due to the linear outer surfaces of the noses 50, thesubstrate 3 is held parallel to the substrate 4. If the substrate 3 ispressed in the direction of the substrate 4, or the substrate 4 ispressed toward the substrate 3, the noses 50 are pressed inwardlyagainst the spring preload 52, as a result of which the substrate 3 canmove in the direction of the substrate 4. During this movement, thesubstrate 3 is guided in a precisely centered manner toward thesubstrate 4 and is held parallel thereto.

[0035] With the illustrated centering pin, the substrates are heldspaced apart by the noses prior to the substrates being joined together.This spaced apart holding or support can alternatively also be effectedby radially outwardly preloaded spheres, spring washers, pins or similardevices that are in a position to hold the substrates spaced apart priorto their being joined together, and to hold them essentially parallel toone another.

[0036] The operation of the inventive apparatus 1 will now be explainedin greater detail with the aid of FIGS. 1 and 2. To load the apparatus1, the housing portions 9 and 10 are moved apart in order to enable ahandling device to place the substrates 4 and 3 upon the plate 34 andthe centering pin 36 respectively. In this connection, the substrate 4,with an adhesive layer 5 that is disposed thereon and faces upwardly, isplaced directly upon the plate 34. The substrate 3 is subsequentlyplaced upon the noses 50 of the centering pin 36 in such a way that thesubstrates 3, 4 are held spaced apart and parallel to one another.

[0037] The housing portions 9,10 are now moved together into theposition shown in FIG. 1, so that the upper chamber 18 is sealedrelative to the surroundings. In this connection, the upper plate 38comes into engagement with an upwardly directed side of the substrate 3,whereby, however, the substrates 3,4 continue to be held spaced from oneanother by the centering pin 36. An underpressure is subsequentlyproduced in the lower chamber 19 by the vacuum pump 22 and the conduit23. At the same time, or subsequently, an underpressure is also producedin the upper chamber 18 by the vacuum pump 26 and the conduit 27. In sodoing there is ensured that the pressure in the lower chamber 19 is lessthan the pressure in the upper chamber 18, so that the membrane isreliably drawn against the support means 42. As soon as a desiredpressure is reached in the upper chamber 18, which pressure prevents airbubbles between the substrates, the pressure in the lower chamber 19 israised in a controlled manner to ambient pressure. As a consequence ofthe thereby resulting pressure difference between the two chambers 18,19, and the lower pressure in the upper chamber 18, the membrane 16,with the plate 34 mounted thereon, is moved upwardly in a controlledmanner to the upper plate 38 into the position shown in FIG. 2. In thisposition, the substrates 3,4 are pressed uniformly together. Due to thefloating mounting of the plate 34, there results a good conformation ofthe plate 34 to the upper plate 38 so that a uniform compressive forceis applied over the substrates.

[0038] The underpressure in the upper chamber is subsequently alsoraised to ambient pressure, so that the membrane 16 with the plate 36 isagain moved downwardly. The two joined-together substrates move with theplate 34 and are released from the plate 38. The membrane 16 comes torest against the support means 42, which prevent the membrane fromsagging downwardly.

[0039] The pressure in the upper chamber 18 is now brought to anoverpressure by the pump 30 and the conduit 31 in order to acceleratethe bonding or curing process of the adhesive 5 disposed between thesubstrates 3,4. Alternatively, the adhesive can also be cured in theapparatus 1 by other methods, such as, for example, a UV irradiation orthe like. Of course, the adhesive can also be cured in a separate curingstation.

[0040] For the removal of the substrates 3,4 that have been joinedtogether in this fashion, the lower and upper housing portions 9,10 aremoved apart in order to provide access for a suitable handling devicefor the removal of the substrates.

[0041]FIG. 4 shows an alternative embodiment of the invention. FIG. 4shows an apparatus 100 for the joining together of two substrates 103,104 that have an inner hole and that—as with the first embodiment—form,for example, a CD or DVD or some other data carrier. In order during thejoining together of the substrates 103, 104 to ensure a gluing togetherthereof, there is applied to the substrate 104 an adhesive 105 in theform of a double-sided adhesive film.

[0042] The apparatus 100 has a housing 107 that is formed of two housingportions 109, 110 that are movable relative to one another and that—asin the first embodiment—each have an essentially U-shaped cross-section.In a moved-together state, the two housing portions 109, 110 formedbetween them a chamber 112 that is sealed relative to the surroundingsat an interface 114 between the two housing portions 109, 110.

[0043] Provided in the upper housing portion 109 is a flexible membrane116 that completely spans the inner region of the housing portion 109and in so doing divides the chamber 112 formed between the housingportions 109, 110 into an upper chamber portion 118 and a lower chamberportion 119.

[0044] The upper chamber portion 118 can be supplied with underpressurevia a vacuum source 122, such as a vacuum pump, and an appropriateconduit 123 in the upper housing portion 109. In a comparable manner,the lower chamber portion 119 can be supplied with underpressure via avacuum source 126 and an appropriate conduit 127 in the upper housingportion 109. The upper chamber portion 118 can furthermore be suppliedwith pressure via a pressure source, such as a pump 130, and anappropriate conduit 131 in the upper housing portion 109.

[0045] A plate 134 is mounted in a suitable manner to the membrane 116and faces the lower chamber portion 119, so that the plate 134 ismovable with the flexible membrane 116.

[0046] Provided on the lower housing portion 110 is a lower plate 138that is disposed opposite the plate 134 and on which is mounted acentering pin 136. The centering pin 136 has the same construction asdoes the centering pin 36 of the first embodiment. The upper plate 134,which is mounted on the membrane 116, has a central opening 140 intowhich the centering pin 136 can move during a movement of the upperplate 134 toward the lower plate 138.

[0047] Provided in the upper chamber 118 are abutment or support means142 in order to limit an upward movement, i.e. into the chamber 118, ofthe membrane 116 and the plate 134 mounted thereon.

[0048] By means of a spring 144, which extends between the upper housingportion 109 and the membrane 116, the membrane 116 is preloaded againstthe abutment or support means 142. The force of the spring 144 isdesigned such that upon pressure equalization in the chambers 118 and119, the spring lightly draws the membrane against the support means 142in order to hold the membrane 116, and the plate 134 mounted thereon, inthe position shown in FIG. 4. Of course, some other preloading devicecan also be provided in order to preload the plates away from oneanother.

[0049] The operation of the apparatus 100 of FIG. 4 is essentially thesame as with the first embodiment, whereby, however, with the embodimentof FIG. 4 there is first produced an underpressure in the upper chamber118 and subsequently in the lower chamber 119 in order to avoid anuncontrolled joining together of the substrates 103, 104.

[0050] A primary difference between the embodiments illustrated in FIGS.1 and 4 is that with the embodiment of FIG. 4, the plate mounted on themembrane is disposed above the plate that is rigidly mounted on thehousing. Furthermore, the vacuum pumps 122, 126, as well as the pressurepump 130, are connected with appropriate conduits 123, 127, 131, whichare all provided in the upper housing portion 109. Thus, in the lowerhousing portion 110 no conduits are formed that communicate with a pumpor vacuum pump.

[0051] The lower housing portion 110 can therefore be embodied in astraightforward and economical manner as part of a rotary switching orindexing table that provides a plurality of these lower housing portions110. The upper housing portion 109 can therefore be utilized for aplurality of lower housing portions 110, thereby increasing thethroughput of the apparatus, since the loading and removal of thesubstrates can be effected beyond the region of the upper housingportion 109.

[0052] Although this is not illustrated in the figures, the plates 134,138 can have suitable surface structures, such as grooves, that face thesubstrates 103, 104 and via which, for example, compressed air can beapplied to the substrates in order to press them together. Suchstructures, which enable a pressing of the substrates together by directapplication of compressed air to the substrates, are already describedin the aforementioned DE 199 27 516.5, which to this extent is made thesubject matter of this application in order to avoid repetition.

[0053] The present invention was described with reference to preferredembodiments, without, however, being limited to the concretelyillustrated embodiments. For example, the shape of the housing candeviate from the illustrated housing shapes. In particular with theembodiment of FIG. 4, it is also possible to make the lower housingportion 110 flat, while the legs of the U-shape of the upper housingportion are lengthened. The plate then enables a sealing with the upperhousing portion 109 to form upper and lower chambers. Furthermore,features of one embodiment can also be utilized in the other embodimentto the extent that these features are compatible. It is also possible toprovide only one chamber to produce a pressure difference on oppositesides of the membrane. For example, it could suffice to supplyunderpressure to one of the plates and the chamber that receives thesubstrates. To prevent an uncontrolled joining together of thesubstrates prior to reaching a prescribed pressure in the chamber, themembrane can, for example via a spring, an electromagnet, or some otherholding device, be held in a position in which the plates are spacedfrom one another.

1. Method of joining at least two substrates together, especially forforming an optical data carrier, according to which the substrates aredisposed in a spaced-apart manner between two plates that are disposedopposite from, and are movable relative to, one another, characterizedin that at least one of the plates, which is connected to a flexiblemembrane, is moved in such a way that a pressure difference is producedon opposite sides of the membrane.
 2. Method according to claim 1,characterized by applying an underpressure in a first chamber thatsurrounds the plates and one wall of which is at least partially formedby the membrane.
 3. Method according to claim 1 or 2, characterized byapplying an underpressure in a second chamber that is disposed on a sideof the membrane facing away from the plates.
 4. Method according toclaim 2 and 3, characterized in that prior to the joining of thesubstrates together, the pressure in the second chamber is held belowthe pressure in the first chamber.
 5. Method according to claim 4,characterized in that the pressure in the second chamber is brought toambient pressure for the joining of the substrates together, while thepressure in the first chamber is held at an underpressure.
 6. Methodaccording to one of the claims 1 to 5, characterized in that the firstchamber is supplied with pressure after the joining of the substratestogether.
 7. Method according to one of the claims 1 to 6, characterizedin that the substrates, prior to their being joined together, are heldspaced apart by a centering pin that engages in an inner hole of thesubstrates.
 8. Apparatus for joining at least two substrates together,especially for forming an optical data carrier, including two oppositelydisposed plates that are movable relative to one another for pressingthe substrates together, characterized in that at least one of theplates is connected to a flexible membrane, and in that an apparatus isprovided for producing a pressure difference on opposite sides of themembrane.
 9. Apparatus according to claim 8, characterized by a firstessentially closed chamber on a first side of the membrane. 10.Apparatus according to one of the claims 8 or 9, characterized by asecond, essentially closed chamber on a second side of the membrane. 11.Apparatus according to one of the claims 9 or 10, characterized by atleast one vacuum source, which is connectable with the first and/orsecond chamber.
 11. Apparatus according to one of the claims 9 to 11,characterized by at least one pressure source, which is connectable withthe first and/or second chamber.
 12. Apparatus according to one of theclaims 9 to 11, characterized by at least one pressure source, which isconnectable with the first and/or second chamber.
 13. Apparatusaccording to one of the claims 9 to 12, characterized in that the platesare disposed together in one of the chambers.
 14. Apparatus according toclaim 13, characterized in that a support means is provided on that sideof the membrane facing away from the plates in order to limit a movementof the membrane and the plate in one direction.
 15. Apparatus accordingto one of the preceding claims, characterized in that the plates aredisposed essentially horizontally.
 16. Apparatus according to one of thepreceding claims, characterized in that the plate mounted on themembrane is disposed above the other plate.
 17. Apparatus according toone of the preceding claims, characterized by a centering pin on one ofthe plates that is introducible into an inner hole of the substrates.18. Apparatus according to claim 17, characterized in that the centeringpin keeps the substrates spaced apart and essentially parallel to oneanother prior to their being joined together.
 19. Apparatus according toone of the claims 8 to 18, characterized in that the plates arepreloaded away from one another by means of a pre-load device. 20.Apparatus according to claim 19, characterized in that the pre-loaddevice includes at least one spring.